Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRICAL CIRCUIT
The present invention relates to an electrical circuit for use in
a spark-ignition internal combustion engine.
In a conventional spark-ignition internal combustion engine,
spark plugs are connected to a high voltage sup?l~ such as an
ignition coil through a distributor. The distributor periodically closes
a conductive path between each spark plug and the coil so as to
enable a high voltage to be applied across a gap definecl by the spark
plug. The high voltage is sufficient to generate a spark between the
electrodes of the spark plug. The clistributor is connected via a
single high tension lead to the coil and by respective high tension
leads to each of the sparlc plugs.
~ great deal of attention has been paid to optimising spark
timing and the conditions within the engine cylinders to which the
spark plugs are fitted. Little attention has been given to the nature
of the spark itself other than to ensure that the spark is sufficiently
large to reliably ignite an air/fuel mi~iture.
It is an object of the present invention to provide an electrical
circuit which enables the spark generated by a ignition coil to
substantially enhance the performance of internal combus~ion engines.
According to the present invention there is provided an
electrical circuit for connection to a high tension lead which is
connected to a spark plug of a spark ignition internal comDustion
engine, the circuit comprising a capacitor the capacitance of which is
such that, if a high voltage pulse is applied to the hi~h tension lead,
the voltage developed across the capacitor and the charge stored by
the capacitor are sufficient to initiate ancl sustain an ignition spark.
Preferably, the capacitor is non-linear, for e~;ample voltage
dependent such that its capacitance reduces ~ith increases in applied
voltage. The capacitor may be temperature dependent such that its
capacitance reduces with increases in operating temperature.
Preferably, a resistor is connected in parallel with the
capacitance. The resistor may be non-linear, for e.~iample ~,-oltage
dependent such that its resistance decreases with increases ir. applied
voltage.
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In embodiments having a temperature dependent capacitor and a
parallel resistor, the resistor may be positioned such that heat
generated in the resistor is transferred to the capacitor.
Preferably, a voltage controlled discharge device is c~nnected
in parallel with the capacitor. A diode may be connected in series
with the capacitor.
A circuit in accordance with the present invention may be
connected in series with a spark plug of an internal combustion
engine, Where that spark plug is energised from a distributor, ~he
circuit may be connected either between the distributor and the
respective spark plug or between a source of electrical energy such
as a coil and the distributor.
In a system in which two or more spark plugs are to be
energised from one source, then a respective circuit may be connectec
in series with each spark plug. For example, in an internal
combustion engine with two spark plugs per cylinder, this rrangement
would circumvent the need for dual ignition drives.
A circuit in accordance with the invention may also be used to
enhance spark performance by connecting such a circui~ between a
high tension lead connected to a spark plug and a source of fi.~ed
potential. Wit'n such c.n arrangement a fuse is preferabiy connected
in series with the capacitor such that if the capacitor or any
component in parallel with the capacitor fails to a low impedance
conductive condition the fuse will burn out and render the circuit
ineffective without disabling the spark plug to which it is connected.
Embodiments of the present invention will now be described, by
~ay of example, with reference to the accompanying drawings, in
which:
Figure l is a schematic illustration of a conventional electrical
ignition system for a four cylinder combustion engine;
Figure 2 illustrates a current versus time waveform for a spark
generated by a conventional circuit of the type illustrated in ~igure
l;
Figure 3 is a general circuit diagram illustrating cor.ponents
which can be combined in a variety of configurations to fomn an
embodiment of the present invention:
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Figure ~ illustrates an embodiment of the present invention
incorporating only two of the components of Figure 3, tha. i s a
capacitor and a parallel resistor;
Figure ~ illustrates a current versus time waveform for a spark
generated by a spark plug connected in a conventional ignition system
such as that illustrated in Figure 1 supplemented by a circuit as
illustrated in Figure 4 connecteci between the coil and distributor:
Figure 6 illustrates a second circuit in accordance with the
present invention;
Figure 7 illustrates a current versus time waveform for a spark
generated using the circuit of Figure 6;
Figure 8 illustrates a further circuit in accordance with Ihe
present invention:
Figures 9 and 10 represent current versus time cu-ves for sparks
generated using the circuit of Figure 8 but at different engine speeds
Figure 11 illustrates a further embodiment of ~he preser~
invention incorporated in a circuit of the type illustrated in Figure
l;
Figure 12 illustrates an embodiment of the presenr invention
incorporated in a conventional circuit but in a differen~ configuration
to that of Figure 11;
Figure 13 illustrates an embodiment of the present inven~ion
used to generate two substantially simultaneous sparks in 2 cylinàer
provided with two spark plugs;
Figure 1~ iliustrates the structure of a capacitor suitable fcr
use in embodiments of the present invention;
Figures 15 to 19 illustrate the effect on output power of fitting
a circuit in accordance with the present in~ention to a conventional
ignition system;
Figure 20 illustrates the effect on hydrocarbon output of fitting
a circuit in accordance with the present invention to a conver.tional
ignition system; and
Figure 21 illustrates the effect on carbon monoxide output of
fitting a circuit in accordance with the present invention to a
con~entional ignition system.
Referring to Figure 1, this illustra~es the basic components of
a conventional coil-energised spark igniticn system. rour s?ark ,~lug5
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1 to 4 are connected between a distributor ~ and a source of fi.~;ed
potential indicated by the earth symbols. The distril~utor; houses a
rotor arm h driven in synchronism with the engine to which the
ignition system is fitted. A high tension lead 7 is connected between
the rotor arm and a standard ignition coil winding 8 wnich in ~urn is
coupled to a source o~ fixed potential indicated by the earth symbol.
Thus when the rotor arm 6 is adjacent a distributor terminal connected
to one of the four high tension leads leading to the spar~; ?lugs,
voltage induced in the coil 8 is supplied to the respective spark plug
and a spark is generated.
Figure 2 illustrates the current versus time relationshi? for a
spark generated by a conventional system such as that iliustrated in
Figure 1. There is an initial "brightline" capacitive discharge
indicated by the line 9 but the spark terminates with ~ . elatively
ineffective inductive flaring portion indicated by line 10.
Referring now to Figure 3, this is a general circuit diagram of
a range of components which can be incorporated in a circuit in
accordance with the present invention. These components comprise
a capacitor 11, a resistor 12 in parallel with ;he capacitor 11, a
voltage control discharge tube 1', a series diode 14 and a parallel
resistor 1~. The reference numerals 11 to 15 are used th,ougnout the
following description where appropriate but it will be appreciated
from the following description that the oniy component which must
always be present in any embodiment of the invention is a ca~acitor
11. Preferably the capacitor 11 is non-linear, having a capacitance
which reduces with applied voltage andjor a capacitance which reduces
with operating temperature. The resistor 12 may also be non-linear,
preferably having a resistance which falls with applied voltage. The
discharge tube 13 is provided simply to preven~ unduly high ~o'tages
being applied to the capacitor 11 and therefore does not normally
affect the operation of the circuit. The diode 1~ is a normal diode
capable of carrying for e.~;ample ~00 rnA. The resistor 1~ is a simple
linear resistor having a resislance of for e~;ample 1 ~lohm and a rating
of 5 watts and 5 kV. The purpose of the circuit ill~strated in general
form in Figure 3 is to alter the current versus time waveform from the
conventional waveform as shown in Figure 2 so as to improve the
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performance of an internal combustion engine to which the circuit is
fitted.
Referring now to Figure 4, this illustrates a first embodiment of
the present invention. The capacitance of capacitor 11 decreases with
the applied voltage. Such characteristics are readily achie~ed with
known ceramic disc capacitors, the relationship between capacitance
and applied voltage being represented b~, a smooth but non-linear
curve. In one practical implementation of the circuit of Figure 4~ the
capacitance of capacitor 11 was 1000 pF at 0 volts, 600 pF at 6 1;~', and
300 pF at 12~ . The resistor 12 is also voltage depenclent. having a
resistance at 0 volts effectively of infinity, a resistance at 6k~ at 12
Mohms, and a resistance at 12kV of 1 ~:lohm.
Referring to Figure :~, this illustrates the current versus time
waveform for a series of sparks generated as a result of introducing
the circuit of Figure 4 between the coil and districutor of a
conventional ignition circuit such as that illustrated in Figure 1. It
will be seen that in the illustrated case three brightline sparks are
generated each of which can contribute to ;he efficiency of
combustion. The less effective inductive flaring part of the spark
shown in Figure ~ is substantially reduced. Thus with the circuit of
Figure 4 the brightline spark is repeated and alternated. Tests have
indicated that the circuit described with reference to Figures 4 and
5 aids combustion particularly in the case of lean fuel ~ ;tures.
In greater detail, when the àistri~utor connects the coil to one
of the spark plugs through the circuit of Figure 4. a primar~ ~inding
(not shown) of the coil is broken by a conventional mechanism within
the distributor and a negative voltage spike of several thousand volts
is transmitted through the capacitor 11 to the spark plug. When the
magnitude of this voltage has risen sufficiently the gap defined by Ihe
spark plug is ionised sufficient1y for a spark to be formed. Current
then flows from the earth terminal of the spark plug through the
circuit of Figure 11, the distributor ~ and the coil ~ to earlh. This
current flow is indicated in Figure 5 by the sharp nega;ive current
flow represented by line 16 and initiated shortly after the start of the
current versus time plot.
The current which passes through the capacitor 11 causes a
voltage ~o ~e developed acrocs the capacitor. As this voltage rises.
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~VO 92~Y048 ~9 PCI/GB~1/01928
the current delivered to the spark plug falls and eventually the
voltage developed across the coil 8 is not sufficient to sustain a
spark in the spark plug gap. Thus the current falls to zero. Or.ce
this has occurred, the combined reverse bias voltage of the coil 3 and
the capacitor 11 is sufficient to re-ionise the gap defined by the
spark plug but this time in the opposite direction. The capacitor then
discharges through the spark gap and this is indicated in Figure 5 by
the line 17. Thus the spark plug is alternatively ionised in one
direction and then in the other and spark current flows in each of
these directions.
Depending upon the engine configuration, the coil. the spark
plug gaps, and the capacitance value of the capacitor 11, the current
may cease after one spark in each3 direction or more cycles of
operation may be sustained.
The resistor 12 has a resistance value sufficiently high as to
have little impact on the united magnitude of the current flowing to
the spark plug. The resistor 12 could have a stable resistance, in
which case its purpose is simply to discharge the capacitor of any
residual charge between successive energisations of the spark plugs.
It is however possible to simplv disperse with the resistor 10. Results
achieved with a simple capacitor circuit with no parallel resistor are
described belo~. It is however preferred to provide the resistor 12
such that its resistance falls with applied voltage.
In the event of a mal~unction. with the circuit of Figure 4 the
voltage across the capacitor 11 can build up to such a high level that
- the capacitor can break down and fail to a low impedance condition.
This does not prevent the circuit continuing to operale in a
conve!ltional manner, that is to say as if the capacitor 11 an~ resistor
12 were absent, but does make the circuit formed by capacitor 11 and
resistor 12 inoperative. To prevent such a high voltage malfunction
occurring it is possible to supplement the circuit as described below
by connecting a threshold voltage discharge device 13 in parallel with
the capacitor 11. The discharee device 13 will be rated to break down
at a voltage above the normal operating voltage of the capacitor but
below a voltage at which damage to the capacitor could occur. Thus
generally the discharge device 13 will be inoperative but it is there
to pro.ect the capacitor 11 if circumstances ar se in ~nich unduly high
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voltages are generated in the coil. The discharge device 13 would be
provided as an alternative to or in addition to the prov, ision of a
non-linear resistor such as a varistor in parallel ~ith the capacitor.
Varistors are available the resistance of which falls linearly with
applied voltage for voltages of a few thousand volts and the
resistance of which falls rapidly at higher voltages, e.g. 12Kv.
The capacitor 11 of Figure 4 e~ihibits a large capacitance to the
brightline edges but its non-linearity with respect to voltage ensures
that it shuts down the less effective inductive flaring components.
The resistor 12 protects the capacitor against overcharging. The
effective capacitance exhibited by the circuit determines ~he frequency
of the brightline edges such that:
frequency = 1/ ~ ~T J ~
where L is the inductance of the high tension coil and C is the
effective capacitance of the circuit.
The circuit of Figure 4 can be used on all conventional vehicles
subject to its use not disrupting other control mechanisms. For
example in vehicles with engine speed counting mechanisms associated
with the ignition system, the multiple ~C sparks per igni~ion cycle
could disrupt engine speed monitoring circuits.
Referring now to Figure 6, this illustrates a further embodiment
of the present invention in which the capacitor 11 is in parallel with
a discharge tube 13 and in series with a diode 14. Figure 7 illustrates
the current versus time spark waveform assuming that the circuit of
Figure 6 is incorporated in a conventional ignition system either
between the coil and the distributor or in each of the high tension
leads leading from the distributor to the spark plugs.
The diode 14 ensures that the circuit retains a DC spark. It
produces an !'echo" brightline discharge to improve the ignition
properties. The echo discharge is indicated by line 19 in Figure 7.
Again, the capacitor 11 is voltage dependent to pass the brightline
edge but also to reduce inductive flaring componen ~s. The circ-lit of
Figure 6 can be used with any engine speed counting mechanism as ~he
spark remains DC. The circuit of Figure 7 is suita~le for use in lean
burn engines.
Referring now to Figure 8, this illustrates an embodimen t of
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using static charge retention. The circuit of Figure 8 comprises
capacitor ll, resistor 12, diode 14 and resistor 15.
Cyclic spark ignition dispersion is caused as a result of the
spark not being of the correct intensity and duration given a
particular engine speed~ Accordingly cyclic dispersion can be reduced
by decreasing the spark intensity and duration at high engine speeds.
Figures 10 and ll illustrate sparl~ waveforms achieved by
incorporating the circuit of Figure 8 in a conventional igni~ion system,
Figure 9 showing the results a~ 2000 rpm and Figure 10 showing the
results a~ 5000 rpm. As can be seen from Figures 9 and 1~, the
ma~imum spark current decreases with increasing rpm as does the
spark duration. The diode 14 does not affect the first brightline edge
indicated by line 20. The resistor 1~ decreases the rate of discharge
of the capacitor ll such that at high rpm the capacitor 11 cannot fully
discharge. The small positive currents indicated in Figures 9 and l0
result from current passing through the resistor. The capacitor 11
thus retains a static charge which is proportional to rpm. This acts
as a barrier to the next spark and therefore reduces its intensity.
Thus the circuit matches the spark shape, intensity and duration to
engine speed.
Referring now to Figure 11, this illustrates a further embodiment
of the present invention incorporated in an otherwise conventional
ignition system of the type shown in Figure 1. In the case of the
circuit of Figure 11, however, the resistor 12 is mounted physically
close to the capacitor ll so that the energ~,- dissipated in the resistor
12 can be used to increase the temperature of the capacitor ll. The
capacitor has a capacitance which decreases with temperature. ~gain
conventional ceramic disc capacitors are well known which e~;hibits
such characteristics.
With such an arrangement, the capacitance of the capacitor ll
reduces as the power dissipation increases with engine speed, that
power dissipation increasing with engine speed. ~s the capacitance
reduces, then so does the amplitude and duration of the spark. Thus
as engine speed increases the spark size reduces, and cyclic
dispersion is reduced as a result of the temperature modulation of the
non-linear capacitor. On the other hand, at lower temperatures the
spark amplitllde is increased which is zls_ beneficial.
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With the arrangement of Figure ll it is necessary to mount the
capacitor 11 and resistor 12 on a heat sinking structure. Power
dissipation in the resistor 12 is typically from 2 to 12 watts. The
capacitor 11 can be arranged to change in capacitance from 1000 p~ to
300 pF over a temperature range of the order of 100C.
The circuit of Figure 11 incorporates a series diode 14 which
enables only DC spark generation. This can be advantageous under
certain circumstances, for example in the case of well maintained and
well tuned engines. This approach reduces the temperature of the
spark plug and the rate of carbon disposition on the plug by reducing
the length and magnitude of the current waveform.
Thus the described circuits enable spark ionisation distribution
in time and space to be optimised. The circuits can be fitted as
original equipment or retrofitted to existing ignition systems. Cyclic
dispersion in firing cycles at different engine speeds can be reduced.
This can lead to improved power, reduced emissions and reduced pre-
detonation, engine knocks and pinking.
The components can be fabricated from conventional material.
For e~;ample non-line~r resistcrs can be fabricated using silicon
carbide (SiC). Capacitors can be fabricated using conventional ceramic
material such as barium titanate.
In the arrangements described with reference to Figures 1 to 11,
the circuit of the invention is connected in series with one or more
of the spark plugs. The circuit is also applicable as an enhancer of
conventional DC sparks in a configuration such as that shown in
Figure 12, in which the same reference numerals are used where
appropriate. In Figure 12, the high tension supply 8, lead 7 and the
plugs 2, 3 and 4 are omitted to simplify the illustration. As shown,
the capacitor 11, resistor 12 and discharge device 1~ are connected in
parallel between a high tension lead 21 connecting the plug 1 to the
distributor; and a fuse 22 which is connected to ground. With this
arrangement, when the coil primary is broken the current initially
flows Ihrough the capacitor 11 from ground until voltage builds up
across the capacitor. The ~oltage builds up to a sufficient level to
cause the plug 1 to spark and thereafter the charge on the capacitor
11 sustains the spark such that the magnitude and duration of tne DC
s~r~; is ennanced. -~
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WO 92/~8(~ PCT/GB91/Olg28
In the arrangement of Figure 12, if the resistor 12 or capacitor
11 were to ail to a low impedance condition, the spark plug 1 would
be in effect short circuited and would be inoperative. If this was to
happen however such a high current would be drawn through the fuse
as to exceed its rating and as a result the fuse 22 would burn nut.
The circuit formed by components 11, 12 and 13 would then be
inoperative and the system would again continue to operate in a
conventional manner. Thus the system fails safe in an operative
condition.
Referring now to Figure 13, this ;llustrates a further application
of the circuit shown in Figure 12. In the arrangement of Figure 13
two plugs 23 and 24 are positioned in the same cylinder of an internal
combustion engine and are intended to fire simultaneously. Such twin
plug arrangements are well known. Each of the plugs 23 and 24 is
connected to a high tension lead terminal Z~ via a respective circuit,
each of the two circuits comprising a capacitor 11, a resistor lZ and
a discharge device 13. ~gain when the coil primary is broken, current
initially flows through the capacitors 11 to cause the plugs 23 and 24
to fire. This arrangement also facilitates the possibility of out of
phase sparks. .~ reverse spark is then induced as a result of charge
building up on the capacitors 11. This arrangement ensures that both
plugs fire reliably and there is no tendency for the firing of one plug
to disable the firing of the other~ Further charge storage could also
be achieved by connecting a further circuit of the type illustrated in
series with the high tension lead connected to the terminal 25.
In the arrangement of Figure 13, a diode could again be
connected between the terminal 25 and each of the circuits but this
would produce uni-directional current thrcugh the plugs.
Figure 14 illustrates the structure of one ceramic disc capacitor
having appropriate temperature and voltage characteristics The
capacitor comprises a disc 26 of barium titanate secured between two
terminals 27 and 28 by a resin casing 29. Such a capacitor will
typically have an outer diameter of 16.5 mm and an axial thickness of
10 mm. The capacitor having the dimensions illustrated in Figure 13
has a capacitance at 12 k~ of 380 picofarads.
Initial tests have been conducted to assess the effect of
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conventional emission systems. The results of these tests are set out
in Figures 15 to 21. In each of the test cases, the circuit was in the
form of a simple ceramic disc capacitor connected between a
conventional ignition coil and a conventional distributor. The
capacitor in each case was applied voltage dependent.
Referring to Figure 15, this shows the relationship between
engine speed and power output for a Ford Sierra car. The lower curve
represents the results with an unmodified ignition system and the
upper curve represents the results of fitting a capacitor in series
with the coil output, the capacitor having a capacitance of 1000
picofarads at zero applied volts.
Referring to Figure 16, this illustrates results obtained with a
Citroen Visa vehicle running on a rolling road. Engine speed is
represented by vehicle speed. The lower curve shows the results of
an unmodified ignition system and the upper curve shows the results
with a modified ignition s!,~stem, a voltage dependent capacitor being
connected in series with the output of the ignition coil and a resistor
being connected in parallel with the capacitor. The capacitor had a
capacitance of ~00 picofarads at zero applied voltage and the resistor
has a resistance of 5 Mohms at zero applied voltage.
Referring to Figure 17, this illustrates the relationship between
power and engine speed in the case of a 1986 Renault 11 GLS. Again
the circuit used was a simple capacitor in series with the coil output.
The lower curve shows results before the circuit was modified and the
upper curve shows results after modification.
Figure 18 shows the results obtained with a Vauxhall Astra car.
The lower curve indicates performance with an unmodified ignition
system and the upper curve shows the effect of connecting a capacitor
in series with the coil output. The capacitor used has a capacitance
of 1000 Pf at zero applied volts.
Figure 19 illustrates results obtained on a rolling road for a
Ford Granada car. The lower curve indicates power with an
unmodified ignition system and the upper curve indicates power after
a voltage dependent capacitor was connected in series with the coil
output. The capacitor had a capacitance of 1000 pF at zero applied
volts.
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Figure 20 illustrates the effects on hydrocarbon emissions. The
upper curve indicates emissions with an unmodified ignition system
and the lower curve indicates emissions after a capacitor was
connected in series with the vehicle coiled output. The capacitor used
had a capacitance of lO00 PF at zero applied volts.
Figure 21 shows the effects on carbon mono~cide emissions
resulting from the same vehicle and the same circuit modification as
generated the results of Figure 20. The lower curve represents
emissions with a modified circuit and the upper curve emissions with
the unmodified circuit. The results of Figures 20 and 21 were obtained
from a conventional ~,'auxhall Astra.
Thus, tests have shown that circuits as described with reference
to the accompanying drawings operate in a par~icularly efficient
manner to provide improved combustion. These improved performance
characteristics arise from the circuit providing enhanced brightline
capacitive discharge components of continuous rising and decaying
edges and more advantageous current waveforms. With circuits not
incorporating a diode, ions impact both plug electrodes thereby
maintaining clean spark plugs. AC excitation also produces better
ionisation. This leads to better start up ignition. ~'here there are
multiple capacitive rising current edges this will help ignite leaner
fuel mixtures. Thus overall better combustion characteristics can be
achieved giving improved engine cleanliness, reduced emissions and
improved engine efficiency. By suitable pulse shaping, the circuit may
also be used to produce current waveforms which lead to a substantial
reduction in radio frequency interference emissions.
In summary, the invention can provide benefits including:
l. A high voltage circuit which produces a dual polarity spark from
a conventional single polarity high tension coil source.
2. A high voltage circuit which enlarges brightline capacitive
components of a single polarity spark produced from a
conventiona! high tension source.
3. A high voltage circuit which produces simultaneous twin, single
or due polarity sparks from a conventional single polarity high
tension source to drive two spark plugs per cylinder
arrangement without the need for dual ignition systems.
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